Reliability in Onboard Computer Systems, Equipment Selection and System Diagnostics

Abstract

When a computer system is used for process control, it is of primary importance to obtain reliability and some degree of fault-tolerance. The process control reliability depends on the computer system design and the back-up philosophy. This paper describes a computer system designed for process control and predictive maintenance onboard a Norwegian gas tanker. A dual computer system which operates in a real time/batch configuration was chosen. This resulted in low software overhead and made it possible to obtain computer backup for the highest priority Jobs.A diagnostic system was developed to detect errors and initiate the necessary operations in case of failure. The diagnostic system consists of both hardware and software parts. High priority diagnostic routines check the hardware and the software parts of the system. In case of errors, the hardware takes the appropriate action.If a system error occurs which affects the process control, the diagnostic system disconnects the output system and establishes a “fail-safe” condition for the process. The system has been in operation onboard the Norwegian tanker, M/T Höegh Multina, since October 1971 and the experience achieved during the first period is reviewed.Finally, ideas are discussed to increase future system availability and insure minimum down time due to hardware failure. Important factors to consider in this case are on-line maintenance diagnostic, printouts to ease trouble determination and location, and permit hardware repair and check-out concurrent with live operations.